I'll be looking forward to seeing your post detailing this build. Are the schematics you posted your "final" build version?
Also, a super newbie/dummy question... the schematic you posted appeared to have 3 separate "pieces." Are those the "power supply board" the "mosfet source follower board" and the "bias board" referenced above? I'm pretty sure I can follow directions well enough to put it together but if you just gave me a schematic and asked me what it was/did I'd be at a serious loss!
of older tube amps -
heathkit, and eico, have 'better iron'.
much better.
sansui amps are are well worth having.
Edcor, might be the 'best' bargain in transformers,
at this point in time ...
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heathkit, and eico, have 'better iron'.
much better.
sansui amps are are well worth having.
Edcor, might be the 'best' bargain in transformers,
at this point in time ...
`````````````````````````````````````````````````````````````
Join Date
14th August 2002
Total Posts
1,500
Blog Entries
11
Wiki Contributions
0
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What a condundrum; I found a reasonably priced ST-70, but I'd prefer to build one from scratch. Hmm...
Hey TubeLab, I love the 68 Camero analogy. It's so appropriate. (I prefer 64-65 Corvettes myself, but I'm not gonna throw a 68 Camero away if I find one for $40 in a garage sale, or even $4000.) Back in 69, the little old lady that lived across he street from us won a 68 Camero in a raffle at the mall. What an agonizing thing for a teenager to watch her driving that beast at 25 MPH to the corner store and back for the next 15 years.
I'm looking forward to the simple PP project. 50 watts sounds about right for me. ;-)
Man I'd love to hear your guitar amp(s). Is that your LP in your avatar? Beauty! I don't like playing them, I'm a strat guy, but I prefer their sound (usually).
..Todd
Hey TubeLab, I love the 68 Camero analogy. It's so appropriate. (I prefer 64-65 Corvettes myself, but I'm not gonna throw a 68 Camero away if I find one for $40 in a garage sale, or even $4000.) Back in 69, the little old lady that lived across he street from us won a 68 Camero in a raffle at the mall. What an agonizing thing for a teenager to watch her driving that beast at 25 MPH to the corner store and back for the next 15 years.
I'm looking forward to the simple PP project. 50 watts sounds about right for me. ;-)
Man I'd love to hear your guitar amp(s). Is that your LP in your avatar? Beauty! I don't like playing them, I'm a strat guy, but I prefer their sound (usually).
..Todd
Yes, unless there are some suggestions to change, it will be final. I will, however, take Sy's advice and wire for triode (take grid with 470R resistor that goes to U/L tap of transformer and wire it to the plate through the resistor instead).
The four sections on the schematic are
1. The signal circuit
2. The B+ circuit, 400 volts with maida style regulator
3. The +75 volts for the positive supply to the MOSFET followers
4. The -105 volt supply to the MOSFET followers, the constant current sinks (the 10M45 circuit at the bottom of the 6SN7 pairs) and the bias supplies.
The MOSFET source followes are the IFR820 devices between the last 6SN7 pair and the 6L6 tube. I think that (Eli?) mentioned that IFRBC20 make a good follower MOSFET too. I have the IRF820s, but I think Tubelab mentioned that they blew in his circuit, so I have placed a zener protection diode between the gate and the source. Hopefully it will prevent that problem.
I am going to try to get all of the power supplies on one board. Real estate may be a problem, so may split the +75 and -105 from that assembly.
The 230:110V transformers that supply the +75 and -105 are units I managed to pick up. You may be able to use different transformers, one option I was looking at was reverse wiring some mains:low voltage transformers from the 5 volt tap.
Cheers,
Chris
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It's just my opinion, but I don't believe that any schematic is final until the amp is built, works good for more than 5 minutes, and you are happy with it.
The amplifier schematic is pretty close since I do have one working. Some component values will ultimately get tweaked to match the chosen output tubes and power supply. Neither one of us has built a working power supply yet. Chris has got his transformers and settled on most of the circuitry. I haven't even decided on how big I want this amp to be yet. I am thinking about making at least two. I have a pair of vintage UTC LS57 OPT's that like Chris's are limited to about 20 WPC. The choices are pretty easy here, likely 6L6GC's in triode. I also have a monster pair of Plitron toroids that are good for 400 watts each! How big of an amp do I want?
Photo of the "breadboard" is included.
I spent a lot of time in high school riding in a friends 68 Camaro convertible. About 10 years later I found out that a friend at work had a dead 68 convertible in his garage. I finally convinced him to sell it to me, and I did the rebuild thing. Out with the 327 / Saginaw, in with the 350 / Muncie. I drove it for about 10 years until my brother convinced me to sell it to him. I did a 66 Mustang convertible after that, and about 10 years ago I started on a big block Challenger. Still not finished.
The Les Paul is an Epiphone. It was a birthday present from my wife several years ago. I also have a Squier Strat, which is easier to play, but the LP has the bluesy sound down right. My guitar playing ability peaked when I was about 15 and has been on a long slow decline ever since. I can't justify any expensive guitars.
I have had probably 50 or so guitar amps over the years, most I have made. They come and go, and right now I have only two. The Simple SE (P-P) and an old Guild Ultraflex. Both are stashed in a warehouse now due to space limitations. There are two other small practice amps stashed in the warehouse too, but both are dead.
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there are several companies selling aftermarket "replacement" power iron for the ST-70, bulked up considerably. A good thing.
the output iron is good.
in input/drive circuit is not good.
the PS "choke" is a goof, as is the amount of PS capacitance. Of course the choke is better than a resistor in the same place, imo.
So what is wrong with the power supply choke?
there are several companies selling aftermarket "replacement" power iron for the ST-70, bulked up considerably. A good thing.
the output iron is good.
in input/drive circuit is not good.
the PS "choke" is a goof, as is the amount of PS capacitance. Of course the choke is better than a resistor in the same place, imo.
So what is wrong with the power supply choke?
I just finished putting 0.59 Farad of new high voltage filter caps, 0.25 Farad of new low voltage filter caps, and a new 5AR4 Rectifier tube on a Hammond H182 organ. It still has an annoying level of quiet hum, and it has two 1 pound chokes, 1 for each rectifier tube. My Dynakit ST-70, with it's wimpy .08F filter cap (20 years old), has less hum and produces louder organ notes from an LP record on dual 10" woofers than the organ does on the same piece with a dual 7591 bass driver,and two dual 6BQ5 treble drivers on a 15" woofer. It's not just the numbers of the materials of your project, it is how it is designed. The organ does have louder treble. Next project: New filter caps for the Triplett 3444A tube tester I fished out of the trash in 1985.
I have some 2400 uF 450 volt caps. They are the size of a quart beer can. You would need 246 of them to make .59 Farad. That would make the filter capacitor about the same size as a minivan. The energy storage capability here is about 60,000 Joules. If you could ever get it charged you would have a big bomb on your hands when the first cap decided to fail.
I have seen two very scary incidents occur when several large capacitors are connected in parallel.
I used to develop extracorporeal shock wave lithotriptors (ESWLs) which are "outside of the body shock wave kidney stone busters". The shock wave generator was basically a giant spark plug inside a 6" diameter steel bowl fed by a giant capacitor directly underneath it. I forget what value the caps were, but they were about 4" dia x about 15" long.
The capacitors were usually used in the power plant industry, and we stored them on metal racks with grounding straps connected to each cap. They were a bit scary looking.
One of the lab techs got "bit" by one and survived; he was fitted with a holter monitor for about 2+ weeks afterward to monitor his cardiac P-wave.
The capacitors were usually used in the power plant industry, and we stored them on metal racks with grounding straps connected to each cap. They were a bit scary looking.
One of the lab techs got "bit" by one and survived; he was fitted with a holter monitor for about 2+ weeks afterward to monitor his cardiac P-wave.
Worse yet, because of the necessary leads, you'd have a nice resonator, not to mention caps with effectively several ohms of ESR. Sort of defeats the purpose...
Dyna Engineers Better than Hammond?
To quote Geek:"indianajo - Too much cap!!!!!!!!
One can't think SS, especially with tube rectifiers
The peak currents will destroy the tube and transformer. "
These 590 uf of caps are the oem values for the Hammond H182, you can look at the prints on captain-foldback.com website. There are 5 can 450 VDC caps, some more atomlytics under the chassis, and a lot of 10 mf bypass caps on the 6 individual preamps plus a 1900 uf of medium voltage elctrolyics I haven't bought yet. 100 VDC powered small signal transistor amps are a weird idea only done about 1968 . The dual 5AR4 rectifiers are British, so probably at least 30 years old, and replacing either with a new Sovtek doesn't change anything, so they are fine. My point is Dynaco eliminated the hum in the ST70 (as far as I can hear) with one 20-20-20-20 uf can cap or 1/8 of what Hammond used to build a noisy (40 year old partially restored) organ. My Dynakit ST70 is 57 years old, but the caps are only 30 years old.
To quote Geek:"indianajo - Too much cap!!!!!!!!
One can't think SS, especially with tube rectifiers
The peak currents will destroy the tube and transformer. "
These 590 uf of caps are the oem values for the Hammond H182, you can look at the prints on captain-foldback.com website. There are 5 can 450 VDC caps, some more atomlytics under the chassis, and a lot of 10 mf bypass caps on the 6 individual preamps plus a 1900 uf of medium voltage elctrolyics I haven't bought yet. 100 VDC powered small signal transistor amps are a weird idea only done about 1968 . The dual 5AR4 rectifiers are British, so probably at least 30 years old, and replacing either with a new Sovtek doesn't change anything, so they are fine. My point is Dynaco eliminated the hum in the ST70 (as far as I can hear) with one 20-20-20-20 uf can cap or 1/8 of what Hammond used to build a noisy (40 year old partially restored) organ. My Dynakit ST70 is 57 years old, but the caps are only 30 years old.
Check out Will Vincent's- he REALLY knows how to build/rebuild Dynaco's!
Dynaco St-70 shiny orange by For Sale | AudiogoN
Dynaco St-70 shiny orange by For Sale | AudiogoN
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